1. Field of the Invention
The present invention relates to a silicon nitride film and a manufacturing method thereof and specifically, to a high quality silicon nitride film and a method for manufacturing the same with comparatively cold temperature. Further, the present invention relates to a semiconductor device that is superior in reliability.
2. Description of the Related Art
There are various electronic device products with technical progress in the world. Conditions required for these products become severe year by year, and long-term reliability is taken for granted as well as enhancing style and performance.
Various elements such as pixels and semiconductor elements are used for such electronic devices, but there are some devices which tend to deteriorate by being exposed to an atmospheric component (such as water or oxygen).
Deterioration of elements forming an electronic device decreases the reliability of the electronic device in itself. Thus, the above described elements which easily deteriorate are often given with protective measures.
There are methods for filling an atmosphere to which an element is exposed, with an inert gas or providing it with a desiccant, as typical protective measures.
In addition, there is a measure that an element that easily deteriorates is covered with a material that does not easily transmit such deterioration factors. As the materials, silicon nitride, silicon oxide, silicon nitride oxide, carbon nitride, carbon are cited. A film made of the materials has barrier characteristics against a particular gas and thus, serves effectively as a protective film for an element.
It is known that silicon nitride has barrier characteristics against moisture or oxygen but the degree is different according to film formation conditions. In general, silicon nitride is denser and has better barrier characteristics, as the etching rate of a particular etching solution is smaller. Further, variation of barrier characteristics is thought to be related to variation of film composition depending on film formation conditions.
By the way, an electroluminescent (EL) element is given as example of the element in which deterioration is promoted by a substance penetrating from the outside like this. Since an electroluminescent element uses an organic material or a combination material of an inorganic material and an organic material as an electroluminescent layer, the electroluminescent element easily deteriorates due to moisture or oxygen.
The electroluminescent element is mainly expected to be applied to displays and the like. However, as the result of deterioration of an electroluminescent element due to oxygen or moisture, generation of a dark spot or progress of a shrinkage is accelerated and the element lacks the reliability as a product and is difficult to practically use. Thus, it is extremely necessary to protect an electroluminescent element from moisture or oxygen and to enhance the reliability.
There is a method for manufacturing a silicon nitride film containing less hydrogen for preventing deterioration of an element due to moisture or oxygen, and the like (Reference: Japanese Patent Laid-Open No. H9-205209).
A barrier film made of a silicon nitride film that does not easily penetrate moisture or oxygen is preferably formed for such an electroluminescent element. Although there are various methods for forming a protective film, plasma CVD is preferably employed since the plasma CVD can give good productivity and coverage.
The barrier film is, however, formed as a top layer, and thus, needs to be formed at the heat-resistance temperature or less of elements formed under the barrier film. For example, when an interlayer insulating film is made of acrylic, the permissible temperature is 100° C. or less in view of problems such as degasification. Naturally, it is not preferable that an EL element is heated at higher temperature than necessary.
However, for forming a silicon nitride film having enough barrier characteristics by a conventional plasma CVD, a substrate is needed to be heated at the temperatures from 300° C. to 400° C., thus, it is difficult to apply the plasma CVD to heat-sensitive elements.